Constitutive Activity of JNK2α2 Is Dependent on a Unique Mechanism of MAPK Activation

• Published in: The Journal of biological chemistry Vol. 283; no. 50; pp. 34935 - 34945
• Main Authors: Nitta, Ryan T., Chu, Albert H., Wong, Albert J.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 12.12.2008; American Society for Biochemistry and Molecular Biology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M804970200

c-Jun N-terminal kinases (JNKs) are part of the mitogen-activated protein kinase (MAPK) family and are important regulators of cell growth, proliferation, and apoptosis. Typically, a sequential series of events are necessary for MAPK activation: phosphorylation, dimerization, and then subsequent translocation to the nucleus. Interestingly, a constitutively active JNK isoform, JNK2α2, possesses the ability to autophosphorylate and has been implicated in several human tumors, including glioblastoma multiforme. Because overexpression of JNK2α2 enhances several tumorigenic phenotypes, including cell growth and tumor formation in mice, we studied the mechanisms of JNK2α2 autophosphorylation and autoactivation. We find that JNK2α2 dimerization in vitro and in vivo occurs independently of its autophosphorylation but is dependent on nine amino acids, known as the α-region. Alanine scanning mutagenesis of the α-region reveals that five specific mutants (L218A, K220A, G221A, I224A, and F225A) prevent JNK2α2 dimerization rendering JNK2α2 inactive and incapable of stimulating tumor formation. Previous studies coupled with additional mutagenesis of neighboring isoleucines and leucines (I208A, I214A, I231A, and I238A) suggest that a leucine zipper may play an important role in JNK2α2 homodimerization. We also show that a kinase-inactive JNK2α2 mutant can interact with and inhibit wild type JNK2α2 autophosphorylation, suggesting that JNK2α2 undergoes trans-autophosphorylation. Together, our results demonstrate that JNK2α2 differs from other MAPK proteins in two major ways; its autoactivation/autophosphorylation is dependent on dimerization, and dimerization most likely precedes autophosphorylation. In addition, we show that dimerization is essential for JNK2α2 activity and that prevention of dimerization may decrease JNK2α2 induced tumorigenic phenotypes.